Week 15 / GI system 1

Question 1

Q: What is the function of the GI (Gastrointestinal) system, and how does it support cellular nutrition?

Answer 1

A: The GI system’s function is to break down ingested food into smaller, absorbable nutrient molecules, which are then absorbed into the bloodstream to supply cells throughout the body with essential nutrients for energy, growth, and repair.

Question 2

Q: What are the main functions of the GI (Gastrointestinal) system?

Answer 2

A: The main functions of the GI system are to:
1. Digest or break down ingested food into small, simple nutrient molecules.
2. Absorb and transfer nutrient molecules, electrolytes, and water into systemic circulation.
3. Make organic nutrient molecules available to body cells for energy (fuel) and as building blocks.

Question 3

Q: What are the five basic digestive processes performed by the GI (Gastrointestinal) system?

Answer 3

A: The five basic digestive processes of the GI system are:
1. Motility
2. Secretion
3. Digestion
4. Absorption
5. Storage and elimination of indigestible food.

Question 4

Q: What is the role of motility in the digestive system, and what are the two types of digestive motility?

Answer 4

A: Motility in the digestive system involves muscular contractions that mix and move the contents of the digestive tract forward. The two types of digestive motility are:

1. Propulsive movements – push contents forward through the digestive tract.
2. Mixing movements – mix food with digestive juices, promote digestion, and facilitate absorption of digested food.

Question 5

Q: What is the role of secretion in the GI (Gastrointestinal) system, and what are the main types of digestive secretions?

Answer 5

A: Secretion in the GI system involves the release of digestive juices in response to neural or hormonal signals. These juices contain water, electrolytes, and organic components (such as enzymes and mucus). There are two main types of secretions:

1. Exocrine secretions – released into the GI tract lumen, including substances like water (H₂O), hydrochloric acid (HCl), bicarbonate (HCO₃⁻), bile, lipase, pepsin, amylase, trypsin, and histamine.
2. Endocrine secretions – released into the bloodstream, including hormones like gastrin, secretin, cholecystokinin (CCK), vasoactive intestinal peptide (VIP), and somatostatin.

Question 6

Q: What is digestion in the GI (Gastrointestinal) system, and how are complex foodstuffs broken down?

Answer 6

A: Digestion is the biochemical breakdown of complex foodstuffs into smaller, absorbable units through enzyme-mediated hydrolysis. The breakdown process includes:
1. Carbohydrates → Monosaccharides
2. Proteins → Amino acids
3. Fats → Glycerol and fatty acids

Question 7

Q: What is absorption in the GI (Gastrointestinal) system, and where does it primarily occur?

Answer 7

A: Absorption is the process of transferring small digested units, along with water, vitamins, and electrolytes, from the GI tract into the blood or lymph. This process occurs largely and most completely in the small intestine.

Question 8

Q: What are the main components of the GI (Gastrointestinal) tract?

Answer 8

A: The GI tract, also known as the alimentary canal, includes two main components:

1. The alimentary canal – a long, continuous hollow tube extending from the mouth to the anus, approximately 30 feet in length.
2. Accessory organs and glands – which include the salivary glands, liver, and pancreas, aiding in digestion and absorption.

Question 9

Q: What structures make up the alimentary canal and accessory digestive organs in the GI system?

Answer 9

A:

1. Alimentary canal – a continuous tube from the mouth to the anus, consisting of:
   
   • Mouth
   • Pharynx
   • Oesophagus
   • Stomach
   • Small intestine (Duodenum, Jejunum, Ileum)
   • Large intestine (Caecum, Appendix, Colon, Rectum)
   • Anus
2. Accessory digestive organs – assist in digestion and include:
   
   • Salivary glands
   • Exocrine pancreas
   • Biliary system (Liver and Gallbladder)

Question 10

Q: How is the GI (Gastrointestinal) system functionally organized [how many parts]?

Answer 10

A: The GI system is divided into three main functional parts:
1. Upper part – Includes the mouth, oesophagus, and stomach. It serves as the food intake source and receptacle and is the site of initial digestive processes.
2. Middle part – The small intestine (duodenum, jejunum, ileum), where the main digestive and absorptive processes occur.
3. Lower part – The large intestine (caecum, colon, rectum), which serves as the storage channel for efficient elimination of waste.

Question 11

Q: What are the four layers of the wall structure of the alimentary canal, and what are their main functions?

Answer 11

A: The wall of the alimentary canal consists of four layers:

1. Mucosa (innermost layer) – Contains epithelial cells, connective tissue, and smooth muscle. Its functions include:
   
   • Protecting against pathogens
   • Secreting mucus, digestive enzymes, and hormones
   • Absorbing digested nutrients into the blood
   • Undergoing rapid cell division and regeneration
2. Submucosa – A dense connective tissue layer with blood vessels, lymphatic vessels, nerve fibers, and lymphoid follicles. Its functions include:
   
   • Providing distensibility and elasticity to the digestive tract
   • Secreting digestive enzymes via glands
   • Regulating gut motility through the submucosal nerve plexus of Meissner
3. Muscularis externa – Composed of inner circular smooth muscle and outer longitudinal smooth muscle. It contains the myenteric plexus of Auerbach. Its functions include:
   
   • Facilitating mixing and movement of food (peristalsis and segmentation)
   • Regulating gut motility through the intrinsic nerve plexus
4. Serosa (outer layer) – A connective tissue and epithelial covering continuous with the mesentery. Its functions include:
   
   • Secreting a slippery serous fluid for lubrication and reducing friction between digestive organs and surrounding viscera.

Question 12

Q: How is the regulation of digestive function mediated in the GI system?

Answer 12

A: The regulation of digestive function is complex and involves multiple mechanisms:

1. Interstitial cells of Cajal (pacemaker cells) – Generate slow-wave potentials (basal electrical rhythms or BER), producing spontaneous rhythmic electrical activity that helps coordinate GI motility.
2. Intrinsic nerve plexuses (Enteric Nervous System, ENS) – Control GI muscle contraction or relaxation by responding to local stimuli.
3. Extrinsic nerves (Autonomic Nervous System, ANS) – Regulate GI contraction and secretion by either increasing or decreasing activity.
4. Gastrointestinal hormones – Influence GI motility and secretion by increasing or decreasing activity.
5. Local sensory receptors – Chemoreceptors, mechanoreceptors, and osmoreceptors detect changes in the GI tract and help adjust digestive processes accordingly.

Question 13

Q: What are the key digestive processes involved in moving food from the mouth to the stomach?

Answer 13

A: The key digestive processes from the mouth to the stomach include:

1. Mastication (chewing) – Breaks down larger food units mechanically, mixes food with saliva containing salivary amylase (which partially digests starch), moistens and lubricates food, and exerts an antibacterial effect.
2. Deglutition (swallowing) – Involves two stages:
   • Oropharyngeal stage – The voluntary phase where food is moved from the mouth to the back of the throat.
   • Oesophageal stage – An involuntary phase where food is propelled down the oesophagus toward the stomach by peristalsis.

Question 14

Q: What happens during the oropharyngeal and oesophageal stages of swallowing?

Answer 14

A:

1. Oropharyngeal stage – The bolus (chewed food) is moved from the mouth through the pharynx into the oesophagus.
2. Oesophageal stage – The bolus is propelled down the oesophagus to the stomach through peristalsis, an involuntary muscular movement.